Steel cables are conventionally used as support means for supporting and/or driving an elevator car in elevator installations. According to a development of such steel cables use is also made of belt-like support means comprising tensile carriers and a casing arranged around the tensile carriers. Such belt-like support means are, similarly to conventional steel cables, guided over drive pulleys and deflecting rollers in the elevator installation. However, by contrast to steel cables, belt-like support means are not guided in grooves in the deflecting rollers or drive pulleys, but the belt-like support means lie substantially on the deflecting rollers or drive pulleys.
In elevator installations, support means do not always run exactly perpendicularly to an axis of deflecting rollers or drive pulleys. The presence of diagonal tension can on the one hand be due to construction or on the other hand be caused by imprecise mounting of the elevator installation. Due to such diagonal tension of the support means there is the risk of the support means laterally slipping off a deflecting roller or a drive pulley. In order to prevent this it is sought to guide the belt-like support means laterally on deflecting rollers or drive pulleys. Thus, for example, use is made of cambered deflecting rollers on which support means of that kind are laterally guided to a certain extent. In order to prevent lateral jumping-off of the belt-like support means use is also made of elevated side edges at the deflecting rollers or drive pulleys. In addition, belt-like support means with longitudinal ribs and longitudinal grooves on the traction surface of the support means as well as on the traction surface of the deflecting rollers or drive pulleys are also known, which ribs and grooves engage and thus ensure lateral guidance of the belt-like support means on the deflecting rollers or drive pulleys.
However, it has proved that measures such as cambered deflecting rollers and drive pulleys, elevated side edges or longitudinal grooves in the support means cannot prevent lateral jumping-off of the support means in every instance. In particular, in the case of support means with longitudinal ribs it was observed that the support means due to diagonal tension was laterally displaced by one or more longitudinal ribs so that the support means protruded laterally beyond the deflecting roller without completely jumping off to the side. There is thus the risk that a support means at least partly jumps off a deflecting roller or a drive pulley to the side without this being recognized at safety systems of the elevator installation.